Complex growth microstructure in Bushveld aureole metapelite:
growing porphyroblasts pseudomorph the microstructure of the matrix
they replace. allowing the detailed sequence of growth to be
determined.

Microstructures and metamorphic reaction processes

The application of thermodynamic methods has revolutionised
many areas of metamorphic petrology, such as the
determination of pressures and temperatures of
equilibration, and yet our understanding of the kinetics of
metamorphic processes has lagged behind. For example, it is
not known, in general, how far evolving metamorphic systems
depart from chemical equilibrium, nor whether reactions
proceed during brief episodes of rapid growth, or are slow,
keeping pace with heat supply.

I developed an interest in
these problems after working on the hornfelses associated
with the Bushveld Complex in the 1980's, and developed a
simple numerical model to study the interaction between
nucleation and growth in metamorphic reactions and its implications for
observable microstructure. In 1996 I
began work again in this area with the help of graduate
student Dan Lovegrove, who returned to the rocks in the
field to constrain and test the modelling.

More recently, prompted by the common difficulty of reconciling the
calculated equilibrium behaviour with the microstructural record in rocks,
my focus has broadened to consider a wider range of processes responsible
for the divergence between observation and calculation, including barriers
to nucleation, sluggish dissolution of refractory phases, and evolution of
the effective bulk composition by fractionation and other processes.

Here you will find (in reverse date order):

2010 - Equilibrium calculation and real
metamorphic process: scenes from a troubled relationship. Invited
lecture given at the Metamorphic Studies Group and at GeoCanada 2010,
with case studies showing varied and informative departures from
predicted equilibrium behaviour.

2003 -
Microstructures of Reaction:
materials relating to the first ISPET Seminar on Microstructural
analysis of Metamorphic Rocks, Venice, October 2003.